Effects of periodic change in pressure and dissolved-oxygen concentration on the incubation characteristics of Pseudomonas aeruginosa

Experiments were carried out to identify an efficient procedure for decreasing the amount of excess sludge in deep aeration columns. Incubation characteristics, especially cellular yield, are closely related to excess sludge, maximum specific growth rate, and chemical oxygen demand. They were measured here for the bacterium Pseudomonas aeruginosa, which tends to be predominant in sewage treatment, at a pressure remaining constant or periodically changing in the range of 1-6 atm (abs.). Cellular yields tended to decrease over 1-2 min pressure cycles; in steady operation they decreased considerably with increasing pressure or dissolved oxygen concentration. Maximum specific growth rates were moderately affected by periodic changes in pressure or dissolved oxygen concentration but markedly affected in the higher concentration range under steady operation. Substrate consumption rates on the other hand, were little affected in either case. The values of chemical oxygen demand ranged from 220 to 250 mg/L, and were thus nearly constant.